The present invention relates to a multiprocessor system for inter-communication of processors, comprising a microprocessor, preferably a determined one of the microprocessors, called central microprocessor, and microprocessors, consequently the other microprocessors, called peripheral microprocessors.
It should firstly be emphasized that the microprocessor qualified as the central microprocessor may not always be the same one, and corresponds to a system in which all the microprocessors are identical and may equally well become this central microprocessor, for example in turn.
However, the present invention is not limited to this concept.
Such multiprocessor systems are encountered in telephony, and in particular in private telephony.
Consider a telephone system constructed around an automatic switch. This automatic switch comprises a connection network by which it may be connected to the different lines of a telephone network, on the one hand, and to the different subscribers' sets, on the other hand. The automatic switch comprises a central unit microprocessor, which may and must be connected to the peripheral unit microprocessors, called junctor cards; these cards each support a certain number of set junctors or network junctors.
In order to more readily understand the communication of the microprocessors according to the present invention, the automatic switch mentioned above and the messages which must for example be exchanged between it and the subscriber junctors in connection with the closure of the loop relays will be considered. A ringing exchange which sends a timed ringing current onto a network junctor of the automatic switch will be considered. The detection of this current is captured by the microprocessor of the card supporting the junctor of the line in question, which must then transfer it to the microprocessor of the central unit which in turn must trigger off the order of closure of the loop relay of the line, via the microprocessor of the card.
More generally, the peripheral processors must carry out the orders coming from the central processor and must shape the data to be transmitted to the central processor.
This may be carried out in real time and by sampling.
However, the more "network" lines, or the more subscribers' sets there are, the longer and heavier the communication of such messages becomes, from the standpoint of implementation.
It has already been proposed to use the memory, with which the microprocessor of the central unit is provided, in direct access mode.
In that case, and upon grant of the central unit microprocessor, the peripheral microprocessors may have direct access to a part of the memory of the central unit. However, this is an expensive solution as a controller is then necessary to write the data into the memory of the central unit microprocessor which, during this time, is stopped, even if such a stop is only of short duration.
It is therefore an object of the present invention to overcome this drawback.